Polymer coated pistons...

[Randy Forbes]

Having a little time in between jobs (not really, but I haven't yet told the next guy that the last car's done...) I was able to spend the entire day today playing with pistons.

Two (2) sets; 100/6 +.040" & 3000 +.060".

The +.060" set needed a few thousandths build up on the skirts (w/TLMB), which is then top-coated with a dry-film lubricant (TLML).

Both sets had their crowns coated with a thermal barrier; well, eleven (11) out of twelve (12) isn't bad...

Masking prior to blasting:

After blasting w/aluminum-oxide:

Skirts built up on +.060" set, and masking pin bores:

All coatings applied, and ready to be cured:

Post cure:

Rhuh-rhoh (naturally, it's a +.060" piston)...:

Chart:

More pictures @: https://www.rfdm.com/gallery/album223

 

[57_BN4]

Hi Randy,

Interesting. In 2005 I designed and built an engine/transaxle for a small racecar competing in FSAE. Because it is a SAE-initiated competition I got to talking with some of the engineers that do the hard yards testing OEM engines and oils n stuff and one of the questions I asked was about thermal coatings. The general response was "we tried em all and none lasted". This is of course for GM/Ford pedestrian engines that need to last 100,000 km without any more than an oil change.

What are your pistons used for and how long are they expected to stay in service?

Incidentally the engine I designed is now in service, albeit in a somewhat different form. Last week it got 3rd in autocross at FSAE-A with zero seat time and no real setup due to the carbon fibre transaxle taking waaay longer to complete than predicted. Then the crownwheel broke its way out of the casing... next year it'll own the place.

 

[Superwrench]

Randy, Sweet ! I might have them for Christmas ! Can't wait to hear it growl ! Thanks! Quick

 

[Randy Forbes]

Hi Randy,

Interesting. In 2005 I designed and built an engine/transaxle for a small racecar competing in FSAE. Because it is a SAE-initiated competition I got to talking with some of the engineers that do the hard yards testing OEM engines and oils n stuff and one of the questions I asked was about thermal coatings. The general response was <span style="font-weight: bold">"we tried em all and none lasted"</span>. This is of course for GM/Ford pedestrian engines that need to last 100,000 km without any more than an oil change.

What are your pistons used for and how long are they expected to stay in service?

Incidentally the engine I designed is now in service, albeit in a somewhat different form. Last week it got 3rd in autocross at FSAE-A with zero seat time and no real setup due to the carbon fibre transaxle taking waaay longer to complete than predicted. Then the crownwheel broke its way out of the casing... next year it'll own the place.

I started using polymer coatings in MGB engines around 1990-1992; at first contracting them out, and then started doing my own application in 1995.

I've had good results, once having the opportunity to pull an engine apart after approximately 80,000 miles (4-cyl MGB).

I always stuck to a pretty ridgid 2500-3000 mile oil change interval, and always with Castrol GTX 10w/40, but the complete lack of component wear was astounding!

While the <span style="font-style: italic">black color</span> had rubbed away from the piston skirts, they looked just like they'd come out of the box__NOT A SINGLE SCUFF MARK ON THEM! I'd never seen that before!

Cam and crankshafts looked great, with no <machine> work required, and even the lifters were still smooth, just showing concentric circles from revolving on the lobes.

I'm sure we'll never see polymer applications as standard features, as they're quite labor intensive to apply. If the application process continues to evolve, that may change, but large-scale manufacturers aren't in the business to produce cars/engines that last indefinitely.

I reassmbled that MGB engine with fresh (Total Seal Gapless) rings, bearing inserts and a valve job, then put it in a different car; it may still be running...

As long as I'm capable, I'll continue to use thermal barriers, thermal dispersants and dry-film lubricant polymer coatings. As much trouble as they are to apply, I wouldn't use them if I didn't see their benefit.

You do know where they were developed, don't you? NASA during the space shuttle program; this was all part of the "technology transfer" that took place in the late 80s/early 90s between NASA and the private sector.

Because of the size of my oven, I tend to run them in batches:

 

[Randy Forbes]

Randy, Sweet ! I might have them for Christmas ! Can't wait to hear it growl ! Thanks! Quick

Christmas might be a bit optimistic (I have to redo the top on one of them) but almost certainly before the end of the year...

 

[RAC68]

Hi Randy,

In preparation for when, if ever, I rebuild my engine, I have been researching the use of thermal barriers as an interesting option. In my conversations, I have heard those who are pro-ceramic and other vintage racers that discount their benefit and seem to indicate a quick skirt ware-off. Since the Healey engine seems to have a looser piston fit than modern cars, I thought applying film on the skirts would tighten the fit and reduce oil use. Also, applying a thermal barrier to the top of pistons would eliminate any chance of overheating as a result of pre-ignition. Are my understandings correct?

Since my head has already been shaved 0.060, I am also considering polishing and relieving the combustion chambers to gain a little space for the coating. How thick is the coating placed on the piston tops and is it the same as the skirt coating?

Thanks,
Ray (64BJ8P1)

 

[Randy Forbes]

The +.060" set required a buildup on the skirts (.0005" a pass) so there was an additional coating on that set. You apply TLMB, then topcoat it with he same TLML that the +.040" set received.

Perhaps the issue over credibility stems from mistaking color with protection?

Yes, when you tear down a coated engine, you don't "see" much of the coating left, but the protection is still there. Did the guys see any scuffed skirts when they were looking for remnnants of the coating? I didn't.

The engine I took apart (MGB w/80k mi) the piston skirts looked like new, nothing at all like the average engine you'd take down. Everything I looked at, I smiled, put back together (fresh rings, and another set of coated mains/rods) and stuck it in another car.

Polymer coatings are a lot of trouble; very labor intensive to apply, requiring lots of pre & post spraying prep. You could understand me doing it for profit (though my margins are really too low), but if I didn't see the benefits, I wouldn't waste the time doing my own engines.

 

[Johnny]

"I reassmbled that MGB engine with fresh (Total Seal Gapless) rings, bearing inserts and a valve job, then put it in a different car; it may still be running..."

What are "gapless rings"???

 

[Randy Forbes]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]What are "gapless rings"???[/QUOTE]Rings without gaps :wink:

 

[Superwrench]

What is a gapless ring ? As Randy has shown, it closes the opening in the ring to stop leakage during the compression stroke. It also helps somewhat on the intake and exhaust stroke as well. The 2 major companies making gapless rings are Total Seal and Childs and Albert. Total seal uses the step ring with a sealing spacer. C and A uses interlocking steps at the gap of the ring. I have used both and prefer the Total seal design, but that is my opinion. I am installing them on my 62 BT-7. I am using a gapless top ring, 1.5 mm 2nd, 3rd rings and 3 mm low tension oil rings. The small metric rings will reduce friction. Friction produces heat and we all know Healeys run Hot ! Randy has coated my pistons and when he ships them and I get this project running I will keep you all posted to how it runs. Have a nice Christmas ! Quick